Method for custom fitting ski boots
United States Patent 3876746

Method for custom fitting ski boots by injection comprises injecting a flowable injection material into a suitable cavity in the boot against a predetermined back pressure, suitably created by air or other gas, and maintaining the back pressure during solidification or retention of the fitting material.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
12/142P, 36/93, 36/117.6, 264/262, 264/269, 425/119, 425/129.2, 425/173
International Classes:
B29D35/00; A43B3/26; A43B5/04; A43B19/00; A43D1/02; (IPC1-7): B29H9/10
Field of Search:
264/222,313,314,223,262,269,40,328,244 36
View Patent Images:
US Patent References:
3744159SPORTS SHOE1973-07-10Nishimura
3736612METHOD OF FITTING SKI BOOTS1973-06-05Check et al.
3632241MOLDING SYSTEM1972-01-04Vanderhagen et al.

Primary Examiner:
White, Robert F.
Assistant Examiner:
Balhoff T. E.
Attorney, Agent or Firm:
Merriam, Marshall, Shapiro & Klose
What is claimed is

1. In the method of custom fitting a ski boot comprising an outer shell, a liner assembly disposed within said shell, said shell and said liner defnining in part at least one cavity therebetween, which method comprises positioning said boot on a foot of a person to be fitted, injecting into said cavity a flowable fitting material, and retaining said fitting material within said cavity, the improvement comprising establishing within said cavity a gas phase having a superatmospheric pressure, injecting said fitting material into said cavity against the back pressure exerted by said gas phase, and maintaining said back pressure at a predetermined substantially constant value until said fitting material is retained within said cavity.

2. The method of claim 1 wherein said outer shell is formed of a substantially rigid material.

3. The method of claim 2, wherein there is associated with said cavity a bladder member adapted to receive said fitting material.

4. The method of claim 3, wherein said back pressure is within the range of about 0.5 to about 4.0 psig.

5. The method of claim 3, wherein said back pressure is within the range of about 1-2 psig.

6. The method of claim 3, wherein said flowable material is thermoplastic and melts within the range of about 120°-180°F.

7. The method of claim 3 which includes as a step preliminary to injecting said fitting material, pressurizing said bladder with a gas to a pressure level consistent with the comfort or performance requirements of the user, noting the pressure level, and injecting said fitting material, maintaining said pressure during injection and solidification of the fitting material.

This invention relates to an improved method for custom fitting ski boots by injection. More particularly, the invention relates to an improved process for custom fitting ski boots by the injection of a flowable fitting material into a cavity within the boot under controlled pressure conditions, so as to achieve equal tightness in the individual boots of a pair or, when desired, a controlled difference in the snugness with which the boots fit.

A type of ski boot which is becoming increasingly popular is a shell, typically made of a substantially rigid synthetic plastic material although other relatively resilient materials such as leather can also be used, into which is fitted a deformable liner which is intended to conform to the individual contours of the user's foot. The outer shell gives firm support to the foot and ankle of the wearer for the purpose of allowing him to obtain precise and accurate edge control of his skis, while the inner liner is intended to provide a snug and firm yet reasonably comfortable fit for the wearer's foot. The rigidity of the outer shell, however, while contributing markedly to the degree of edge control which can be obtained with boots of this type, creates a problem with respect to fitting of the boots. Whereas formerly-used leather boots can usually stretch somewhat in use to accommodate themselves to the wearer's feet, outer shells made of rigid plastic materials are unyielding, and therefore the only control which can be used for proper fitting is the size, shape, and resiliency of the liners.

The problem involved in fitting plastic boots is twofold. On the one hand, the wearer's foot must be held snugly and firmly within the boot in order to permit the desired degree of edge control, yet at the same time localized pressure areas against the wearer's foot must be eliminated in order to provide a reasonable degree of comfort. The fact that skiers' feet may vary widely in contour, even when of the same nominal size, creates a problem in fitting such boots using liners in a few stock sizes.

One of the solutions to the problem of custom fitting rigid plastic boots has been to provide the liner of the boot with one or more cavities into which there is injected a flowable material while the boots are being worn by the ultimate user. The flowable material adapts the liner precisely to the contours of the wearer's foot and when solidified or otherwise retained in the cavity produces a snug and firm yet comfortable custom fit.

The flowable materials used to adapt the outer shell of the boot to the wearer's foot can be, for example, those described in A. W. Hanson's U.S. Pat. Nos. 3,237,319 and 3,402,411 or in the pending application of A. B. Hanson et al., Ser. No. 216,080, filed Jan. 7, 1972. These materials can be wax; foamed-in-place materials such as polyurethanes; liquids such as mixtures of ethylene glycol or polyethylene glycol with water; air; partially gelled hydrocarbon materials; thickened aqueous or hydrocarbon materials; and the like. In some instances it may be desirable to use combinations of these materials, and in addition, heating of some of the materials to obtain appropriate flowability properties may be desirable or necessary.

Custom fitting of ski boots by the injection of a flowable fitting material, however, presents the problem that the person being fitted is called on to judge subjectively the tightness of fit, especially the equality of tightness in each boot of a pair. The method of the invention removes a great deal of the uncertainty involved in custom fitting ski boots by injection, and permits equal tightness in both boots of a pair to be readily obtained. In addition, the method permits the fitter to achieve a proper fit for a beginning skier who may have no knowledge of how tight properly fitting boots should feel.

In accordance with the method of the invention, the flowable material used in fitting is injected into the boot under conditions of controlled predetermined back pressure, which is maintained while the flowable material solidifies, or until the inner liner is sealed to enclose the material, whereby there is produced as desired a controllable and uniform degree of tightness in each boot of a pair, or greater tightness in one boot as desired or necessary to meet special conditions.

The invention will be better understood from the following detailed description thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an isometric view in partial section of a typical boot suitable for use in the invention, the boot having a liner provided with a cavity into which the flowable fitting material is injected; and

FIG. 2 is a partially schematic diagram of one embodiment of apparatus useful in carrying out the process of the invention.

The boot shown in FIG. 1 is a typical boot of the type with which the process of the invention is concerned. The boot shown in this figure is disclosed in the copending patent application filed on Jan. 7, 1972, Ser. No. 216,080, for Alden B. Hanson and Chris A. Hanson. As described in that patent application, the boot consists of an outer shell 10 made of a substantially rigid plastic material which is provided with a rearwardly opening tongue member 11 through which access to the interior of the boot is obtained. The tongue member 11 is closed and held in position by means of loops 12 which engage buckles 13 on either side of the boot. Into shell 10 is fitted inner padding member 14 which provides both padding for comfort of the wearer and the capability to custom fit the boot to the wearer's foot. Inner padding member 14 has an outer surface which is generally complementary to the inside of shell 10, while the inner surface of inner padding member 14 is adapted to surround and generally conform to the wearer's foot and ankle. The rear portion of inner padding member 14, in the vicinity of tongue member 11, is cut away so as to provide access to the interior of the boot. Tongue member 11 is lined with a tongue liner 16 which in conjunction with inner padding member 14 essentially surrounds the foot of the wearer with a padding layer.

Inner padding member 14 is provided with a cavity 17 in its outer surface which in conjunction with the inner surface of shell 10 defines a zone into which a flowable material can be injected in order to force inner padding member 14 into exact conformance with the contour of the wearer's foot. In a preferred embodiment, as illustrated in FIG. 1, a thin bladder member 18 is shaped to fit the cavity between inner padding member 14 and outer shell 10. As shown in the figures, bladder 18 is shaped to extend from one side of the wearer's foot over his instep to the other side. In addition, bladder 18 is provided with a pair of tubes 19, 19a used for filling the bladder with flowable material. Although a single tube may be used for this purpose, it is generally desirable to use a pair of tubes, one of which is used to inject the flowable material while the other permits the escape of air.

FIG. 2 illustrates schematically one embodiment of the apparatus which can be used to carry out the method of the invention. It should be understood that the specific apparatus disclosed in this figure is illustrative only and any other apparatus having an equivalent function can also be used. As shown in FIG. 2, injection gun 21, filled with a flowable material which in the case of a thermoplastic substance suitably can have a melting point within the range of about 120°-180°F, is provided with control valve 22 at its exit end and is attached to one of the filling tubes of the boot, e.g., 19. The other filling tube 19a is connected by tube 23 to a hermetically sealed, gas pressure-tight overflow conduit or container 24, which is also provided with pressure gauge 26 and a rubber squeeze bulb 27 equipped with bleed valve 28. All of the connections between individual components are hermetically sealed so that a superatmospheric gas pressure can be built up within the system.

The method of the invention has as an essential element the establishment and control of a predetermined substantially constant back pressure on the flowable fitting material while it is being injected into the boot and during the solidification or final containment thereof. As a preferred initial step in the process, the bladder element of the boot is pressured with gas, such as air, rather than with the flowable material which is ultimately used, to a pressure level which the wearer of the boot agrees is comfortable while providing a sufficiently snug fit for proper edge control. At this time the gas pressure is noted, and the flowable material is then injected into the boot, maintaining the predetermined back pressure until the material hardens or is finally contained. In this way the degree of snugness which was selected by the skier is obtained and in addition the same degree of tightness can be obtained in each boot of a pair. With a beginning skier, the fitter may suggest a pressure level which he believes to be adequate from his experience.

The procedure typically followed in custom fitting a pair of ski boots in accordance with the method of the invention is as follows. With the foot of the wearer in place within the boot (as shown in phantom outline in FIG. 2), control valve 22 is closed and the squeeze bulb 27 is operated to build a superatmospheric pressure in the system consisting of bladder 18, overflow container 24 and the associated connecting tubing. The pressure which is built up within the system is measured by means of pressure gauge 26. Pre-pressurizing with air in this manner serves the advantageous function of indicating to the user the degree of tightness which is created by a given pressure level. It is advantageous to produce initially a pressure which is substantially in excess of that to be used and then to reduce gradually the pressure through bleed-off valve 28 until the proper pressure level has been reached. Over-pressurizing in this manner demonstrates the effect of too tight a fit and in addition serves to straighten out the bladder 18 within cavity 17 between the inner liner 14 and shell 10, thereby preventing the possibility of improper or incomplete filling of the bladder with fitting material.

The desired pressure level within the system having been established, control valve 22 is opened and flowable thermoplastic fitting material is injected by means of injection gun 21 or other suitable pump means through filling tube 19 into bladder 18. The fitting material is injected steadily while the wearer moves his foot gently within the boot until an overflow of fitting material issues from exit tube 19a into overflow conduit or container 24, which is suitably transparent. Alternatively, a transparent section may be placed in tube 23 which would show the passage therein of excess fitting material. During the entire filling operation the air pressure is monitored on pressure gauge 26 and appropriate corrections in the pressure are made by manipulating bleed valve 28 as necessary. While the degree of back pressure is determined by the wearer of the boots, it will be generally found that pressures in the range of about 0.5 to 4 psig., and particularly about 1-2 psig., will be suitable for proper fitting in most cases.

As alternatives to the manual operation of bleed valve 28 during injection, there can also be used an automatic pressure control valve set at the desired pressure or a dip tube in a column of a suitable liquid such as mercury, water or a suitable salt solution. Although mercury can be used for this purpose, the health hazards which may be created if mercury is spilled may make such use unsuitable. Water can be used, but the column necessary to create the suitable back pressure might be inconveniently high (up to about 8 feet). A suitable liquid for use in a dip-tube pressure regulating system for this use is a solution of zinc bromide, which can be dissolved in water to an extent of about 80% by weight to give a solution having a specific gravity of about 2.7. Such a pressure-regulating system employing a solution of zinc bromide need be only approximately 3 feet in height to cover the highest back pressure which might be used.

The use of a pressure-regulating valve or equivalent can be eliminated entirely by making overflow conduit or container 24 large, e.g., 50-150 times the volume of the bladder, or by incorporating an auxiliary volume of such size in the system. With the desired back pressure established in the system at the start, injection of sufficient fitting material to fill the bladder will cause only an insignificant rise in the pressure of the system.

Although in the preferred embodiment the boot is provided with bladder 18 within the cavity 17 defined by liner 14 and outer shell 10, it is also possible to carry out the method of the invention with a boot in which the cavity is defined solely by the liner and the shell. In such case, it will be found desirable to cement the liner to the shell with particular attention to avoiding any possible openings which would prevent the establishment therein of the necessary back pressure. Suitable inlet and outlet orifices to the cavity can be made in any appropriate manner, as will be apparent to those skilled in the art.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.