US1411822A - Pencil lead - Google Patents

Description

UNITED STATES PATENT cranes.

CHARLES E. WEHN, OF ALAMEDA,, CALIFORNIA.

PEN GIL LEAD.

No Drawing.

T o all whom it may concern.

Be it known that I, CHARLES E. WE N, a citizen of the United States, residing at Alameda, in the county of Alameda and State of California, have invented a new and useful Improvement in Pencil Leads, of which the following is a specification. This invenion relates to pencil leads and the means of adapting them to fit into and be held in pencil holders of the character in which the lead is fed forward for use as desired. More particularly the invention pertains to a means whereby the diameter of leads and the like may be slightly increased by the application of a semi-hard coating material and a frictional resistance produced.

Ordinary pencil leads in use today consist of a composition of graphite, paraliine, clay or similar earthy substances. These ingredients are finely ground and thoroughly mixed in certain proportions, the proportions employed depending of course upon the degree of hardness or color desired. A

dough-like material is in this manner formedwhich is passed through molds or dies of uniform diameter and is in this manner reduced to the desired shape and diameter. The molded material is next dried and is then'plaoed in ovens where the leads are baked under high temperature for a considerable time period. The leads are finally removed and cooled and the manufacturing operation may in this instance be considered completed.

Minute examination of the leads, whether of one composition or another will show a considerable variation in exterior diameterv and the cause of this variation may be traced to difierent sources, for instance, some manufacturers mold the leads by passing the dough-like, composition under high pressure through a die. This die is subject to considerable wear and the diameter of theleads is thus gradually increased until the increase is so great that renewal of the die is necessitated. Again shrinkage takes place during the drying and baking oper-' ation, and the shrinkage of course varies with the composition. Hence it is found in actual practiw that the leadsvary from two to three thousandths of an inch in -diameter and a uniform-product cannot be obtained except by the grading of leads when completed. This variation as previously stated is slight and is neither noticeable norv Specification of Letters Patent.

Patented Apr. 4, 1922.

Application .filed February 24, 1920. Serial No. 360,963.

detrimental when the leads are cemented and permanently lncased by wood, as in ordinary pencils, but it presents an entirely different problem when the leads are placed in what ma fillable pencils of different makes. Pencils of this character are usually provided with a lead holder in which is formed a lead receiving passage and. a feed mechnism whereby the lead is gradually advanced when WOIIL. The leads in certain forms of pencil are held in the holder or receiving passage solely by snug fit or frictional engagement, whlle other makes of pencils are provided wlth mechanisms for increasing or decreasmg the diameter of the lead receiving pas-' sage, or for clamping the leads 'therein, such mechanism being provided with no other object in view than that of taking care of the slight variation of the exterior diameterof the leads. Most pencils of the .character described are however provided Y pencil inoperable as the leads cannot'be retained and will therefore fall out.

The purpose of the present invention is to overcome the above objections, for instance, the elimination of mechanical means for increasing or decreasing the diameter pf the lead receiving passage or of providmg means for clamping the leads therein, and further eliminates the necessity of grading, the main object being to always insure a snug fit and to produce a frictional resistance of the leads in the holders whether the diameter is under or above size. This is accomplished by coating the leads with a semi-hard substance such as wax, paraffine and the like. This coating material is applied in any suitable manner, for instance, by dipping the leads in parafiine. The material when hardened presents a semi-hard friction producing coating which slightly increasesthe diameter of the leads, that is at least to such'an-extent that a snug fit will be formed between the leads and the holder in which they are. inserted regardless of ylz'hether the leads were originally too sma An important feature of the present inbe termed mechanical or resize or of proper diameter, for instance, if a coated lead of proper diameter is inserted, it is obvious that the coating material, due to its semi-hard nature will be scraped off or removed when the lead is inserted, similarly that the coating on leads of smaller diameter may be only partially removed and in extreme instances not removed, the thickness of the coating material being such that it will form a filler between the interior surface of the. lead receiving assage and the lead proper and is under all conditions so soft that any excess material is easily removed when the leads are inserted. A snug fit is' in this manner obtained whether the leads are oversize or undersize and a frictional resistance is produced, thus mechanical contrivances for securing the leads will therefore be entirely eliminated. The cost of manufacture is in this manner reduced and a simple and easily operable pencil becomes possible.

For the purpose of this specification, it is assumed that the apertures of mechanical pencils or the holders which are to receive the lead are of substantially uniform diameter, while the leads, as above'described, are of non-uniform diameters. .Therefore the invention is the adaptation of means whereby leads of non-uniform diameters are brought to uniformity. In carrying out this object it is preferable to'build up the undersized non-uniform leads to oversize by the medium of a skin covering which is not only softer than the lead but has sufiicient inherent rigidity or. hardness and sufiicient permanence that it is readily reduced to the desired size under conditions of actual use in the holder.

Having thus described my invention, what I claim and desire to secure by Letters Patent is-- c An article of manufacture consisting of pencil leads having an exterior coating of parafiine.

' In testimony whereof I have hereunto set my hand in the presence of two subscribing witnesses.

CHARLES E. iWEHN. Witnesses:

JOHN H. HERRING. W. W. HEALEY.