Mechanical pencil lead protection pipe with protuberance

Details Mechanical pencil lead protection pipe with protuberance Mechanical pencil lead protection pipe with protuberance

1990-10-04

1992-02-04

Bratlie, Steven A.

Coating implements with material supply

Solid material for rubbing contact or support therefor

Including means to advance material

401 80, 401 86, 401 87, B43K 2122

Patent

active

050855344

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to a mechanical pencil capable of utilizing efficiently a refill or a writing lead.
When a writing lead becomes short in conventional mechanical pencils, the lead is released from a chuck holding it such as a three-split chuck, a ball chuck. The lead released from the chuck remains between the tip of the chuck and the tip of the mechanical pencil (lead protection pipe). The lead thus left (hereinafter referred to as the "remaining lead") is merely held lightly by a lead detent. Therefore, if writing is made by this remaining lead portion, the lead rotates freely during writing and the feel of writing drops. It is therefore customary to discharge the remaining lead by pushing it by a subsequent lead or to pull it out and to discard. This phenomenon can be observed more remarkably in the case of the remaining lead which comes off from the lead detent and eventually, the lead is likely to fall.
Various proposals have so far been made in order to use up or minimize the remaining lead to use it effectively. Typical examples are as follows. A first proposal is disclosed in Japanese Utility Model Publication (Unexamined) No. 56-115284/1981, wherein the tip of the lead protection pipe is made non-round in its sectional shape by drawing it by a press, or the like. A second proposal is disclosed in Japanese Utility Model Publication (Unexamined) No. 53-109934/1979, wherein the tip of the lead protection pipe is provided with a slot and is contracted. A third is disclosed in Japanese Utility Model Publication No. 58-32959/1983, wherein a flexible thin film made of rubber or the like is integrally laminated on the inner surface of the lead protection pipe.
There are two functions required for the lead protection pipe in order to make effective utilization of the remaining lead. First, the lead protection pipe does not permit the fall of the remaining lead when it stays in the lead protection pipe (or in other words, the pipe must have the lead retaining function). Second, the lead protection pipe does not permit the rotation of the remaining lead when writing is made by use of it (or in other words, the pipe must have the writing function by the remaining lead).
The device disclosed in Japanese Utility Model Publication (Unexamined) No. 56-115284/1981 described above has the writing function by the remaining lead. However, this device is not free from the problems in that the lead is likely to rotate unless the drawing inner diameter is made sufficiently small because the lead protection pipe is drawn, variance of inner diameters is likely to occur and if the inner diameter becomes too small due to this variance, the lead is held back and cannot be fed normally. In other words, the device involves the problem of dimensional accuracy for satisfying the lead retaining function.
The device disclosed in Japanese Utility Model Publication (Unexamined) No. 53-109934/1978 described above has the writing function by the remaining lead in the same way as in Japanese Utility Model Publication (Unexamined) No. 56-115284/1981 described above. However,since fins are formed at the time of slotting, the feed of the lead is likely to be prevented by the fins and a step of removing the fins becomes necessary, with the result that productivity drops.
The device of Japanese Utility Model Publication No. 58-32959/1983 has the lead retaining function because the flexible thin film is integrally laminated. However, since the lead is retained by only the force of frictional resistance of the flexible thin film, there remains the problem that the remainig lead is rotated at the time of writing by use of the remaining lead. In other words, the writing function by the remaining lead of this device is not sufficient.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide a mechanical pencil which has both the lead retaining function and the writing function with the remaining lead and which can make effective utilization of the remaining lead.
The present invention pro

REFERENCES:
patent: 4281939 (1981-08-01), Mitsuya

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